In recent years, a technology of forming a thin film transistor (hereinafter referred to as “TFT”) on a substrate has been largely forwarded, and applications to active matrix display devices are in progress. In particular, since a TFT that uses a polysilicon film is higher in the field effect mobility (also called as “mobility”) than that that uses an existing amorphous silicon film, a high-speed operation can be realized. Accordingly, pixel control that is so far driven with a driving circuit outside of a substrate is enabled to carry out with a driving circuit formed on the substrate same as that of the pixel.
In such an active matrix display device, since various circuits and elements can be formed on the same substrate, various kinds of advantages such as reduction of manufacturing cost, miniaturization of a display device, an increase in manufacturing yield and a decrease in throughput can be obtained.
Furthermore, a study of an active matrix type EL display device that has an electroluminescent element (EL element) as a self-emitting element is actively forwarded.
In general, a current value that is flowed to an EL element and brightness of the EL element are in proportion. Accordingly, a pixel configuration that is different from that of a LCD in which the brightness is controlled through a voltage value, in particular, a pixel configuration that controls the brightness through a current value is proposed (patent document 1).
Furthermore, at the same time, in order to control the brightness through the current value, devises are necessary not only for the pixel but also for the driving circuit. Accordingly, various driving circuit configurations have been proposed (patent document 2).
An example of the driving circuits, as shown in FIG. 9A, is constituted of a shift transistor part constituted of DFFs, a NAND circuit, and a buffer circuit constituted of inverters. A general example of a timing chart of the driving circuit is shown in FIG. 9B. In this circuit configuration, a pulse shifts in accordance with a CLK synchronization signal.
(Patent document 1)
WO 01/06484 pamphlet
(Patent document 2)
WO 02/39420 pamphlet